Serine proteases, and specifically those expressed in prostate epithelium, have emerged as important molecules of relevance for understanding the pathophysiology and mechanisms of the prostate cancer metastatic process. Further, the enzymatic activities of these proteases when expressed in ectopic locations such as in the bone may alter the local environment to favor tumor cell invasion and growth. The aims of this proposal are based upon the hypothesis that: Progression to metastatic prostate cancer is driven by the persistent in situ and ectopic expression of membrane-bound serine protease enzymes TMPRSS2, hepsin and matriptase. These serine proteases influence metastatic disease through protease action on barriers to invasion (e.g. extracellular matrix) and reciprocal alterations in signaling factors derived from the tumor and microenvironment (e.g. IGF, HGF, CXCL12). The specific aims of this proposal are: Aim 1. Define the biological substrates of the TMPRSS2 protease, compare the substrate specificities with hepsin (and other proteases), and identify inhibitors of TMPRSS2 function (Collaboration wth Project 3). Aim 2. Determine the cellular signaling pathways influenced by TMPRSS2 activity and identify the attendant phenotypic responses that modulate tumorigenic characteristics of proliferation, migration, and invasion. Initial studies will focus on IGF, HGF, and CXCL12 signaling. (Collaboration with Project 3). Aim 3. Determine the biological role(s) and molecular mechanisms by which TMPRSS2 influences prostate cancer cell dissemination and growth in the bone environment (Collaboration with Project 1). Completing the specific aims of this proposal will determine mechanisms by which TMPRSS2 influences prostate cancer cell invasion and metastasis, and will develop model systems and reagents suitable for exploiting TMPRSS2 as a therapeutic target. RELEVANCE (See instructions): The lethal form of prostate cancer manifests as disseminated disease to bone and other sites. We have determined that a membrane-anchored serine protease, TMPRSS2, modulates features of prostate cancer metastasis. This proposal is designed to determine the mechanisms by which TMPRSS2 contributes to invasive and metastatic growth, and identify inhibitors capable of abrogating TI\/IPRSS2 function.